In modern vehicles there is a tendency towards increasing electrical and electronic equipment resulting in a growing consumption of electrical energy. This makes it advisable to increase the current nominal voltage of the vehicle's electrical system by up to three times, that is, from the current 14 V DC to 42 V DC. However, due to the conveniently calculated and designed current manufacturing and installation infrastructures of electrical systems which already exist in the automotive industry, a sudden transition from one voltage to another is made very difficult.
Increasing the voltage (Volts.) threefold (42 V) involves the reduction of current (A) for the same amount of power. Less amperes mean smaller cable cross-section for supplying current, less weight and lower consumption.
A solution has been proposed in order to avoid said sudden transition, which consists of implementing an electrical and electronic distribution system architecture for the vehicle using networks operating at two different voltage levels, which has been called “dual voltage system”. Thus, some components will continue to work at 14 V as until now, so that it will not be necessary to introduce changes in their electrical control and distribution networks, while other components will come to work at 42 V with a more appropriate output and/or optimisation of their performance.
Said dual voltage system may be basically achieved in two ways: either with a single 42 V battery and a unidirectional DC/DC voltage converter from 42 to 14 V; or with two 14 and 42 V batteries respectively, and a bi-directional DC/DC voltage converter from 14 to 42 V or vice versa.
The voltage converter is a key part of the new system in any of the solutions.
Patent WO 97/28366 is an example of the utility of having a dual voltage system in automotive vehicles, describing an ignition system for internal combustion engines which uses a dual voltage electrical supply with a higher voltage to produce a high-intensity electric arc and a lower voltage to cause ionisation. A signal controller analyses the ionisation signal to determine a series of parameters concerning the correct operation of the ignition.
Patent WO 95/13470 describes another ignition system for internal combustion engines supplied by dual voltage supplied by a single supply source and subsequently dualised by a DC/DC voltage converter.
Patent EP-A-0892486 describes an unidirectional voltage converter device to supply dual voltage from a single supply source.
The introduction of the new architecture of the dual voltage system in automotive vehicles carries with it an increase in the complexity of electrical networks. As mentioned hereinbefore, the system includes one or two accumulators or batteries, a voltage converter and one or more distribution boxes in which electronic signal and power control means are centralised, comprising a microprocessor and electrical protection means. The vehicle also comprises an electric generator, usually an alternator, which supplies current to the accumulator or accumulators by means of a rectifier, and which also directly supplies most of the components when the vehicle is running.
Until now, the voltage converter has been situated at some place in the electrical networks, separated from the distribution box or boxes. However, this arrangement has several drawbacks such as: an increased connection cabling which on one hand means a greater voltage drop and on the other hand affects the manufacturing cost, the vehicle's weight and accordingly the fuel consumption; a greater volume occupation inside the already scarce space of the engine compartment; an increased number of component fixing points to the vehicle with greater complexity of assembly; an increase in the number of electrical components exposed to vibrations, which reduces the system's reliability; a redundancy of systems, for example, a microprocessor for the voltage converter and a microprocessor for the distribution box; greater difficulty for thermal dissipation of components arranged in separate boxes; greater difficulty in achieving electromagnetic compatibility due to the incorporation of cables which provide high frequency emissions which produce interference in the components of the distribution box.
References to the subject and objects of this invention are also found in different publications among which the following may be mentioned: J. G. Kassakian “Challenges of the new 42 V architecture and progress on its international acceptance” VDIBerichte 1615, 1998 Baden—Baden; “Road vehicles—Conditions for electrical and electronic equipment for a 42 V powernet—Part 1—General, 42V Working Draft Work Group “Standardization” 1999-Feb.-12, 2000-Apr., “Draft specification for 42 V battery in a 2-voltage vehicle electrical system for BMW and Daimler-Benz SICAN” 29.6.98; MIT Auto-Consortium-42V Net Research Unit #1 “DC/DC converters for Dual Voltage Electrical Systems”.
DE-A-19645 944 discloses a control device for an onboard electrical system with at least two batteries which can be charged by a generator and serve to supply various consumers, the control device including a supply netweork element, a bus-capable microcomputer, a direct voltage converter and a short circuit proof end stage.
EP-A-337155 discloses an electrical system for a motor vehicle with two series connected batteries in that two individual mutually independent generators or ta dual generator with two systems for example 12 volts/24 volts is used for voltage generation.
U.S. Pat. No. 5,801,925 the essential features of which are included in the preamble of claim 1, describes an automotive junction box for controlling the flow of power and control signals throughout the interior of an automobile having controllable features and including a casing with separated circuit boards for carrying power from and through the housing and for relaying control signals from the housing for actuating the features.